Method of operating internal combustion engine including electromagnetically driven intake valves

ABSTRACT

A method of operating an internal combustion engine having an; electromagnetically driven intake valves for a vehicle. With the method, deviation of an opening operation of the electromagnetically driven intake valve in response to a command signal for opening the intake valve from a predetermined characteristic is detected, and at least one of parameters used for controlling operation of the internal combustion engine is corrected so as to reduce a change in an intake air charging state in which the internal combustion engine is charge with the intake air. A valve closing timing of the intake valve or a valve closing timing of the exhaust valve that cooperates with the intake valve may be used as parameters to be corrected.

BACKGROUND OF THE INVENTION

1. Field of Invention

The invention relates to a method of operating an internal combustionengine of a vehicle, and more particularly, to the method of operatingan internal combustion engine having an electromagnetically drivenintake valve.

2. Description of Related Art

Conventionally intake valves or exhaust valves of an internal combustionengine have been operated by a cam of a cam shaft that is driven by acrank shaft synchronously. Recent advancement in a control technologyusing a computer has allowed operation of the intake or exhaust valvesby an electromagnetic actuator. The resultant expanded range of thevalve operation timing makes it possible to control operation of theinternal combustion engine especially for a vehicle in various modes.The aforementioned technology for controlling the operation is disclosedin JP-A-2000-73800, 2001-182570, and 2001-193504, for example.

FIG. 1 is a schematic cross sectional view of the electromagneticallydriven intake valve that corresponds to the view shown in FIG. 2 of JP-A2001-193504. Referring to FIG. 1, an intake port 26 has an open endaround which a valve seat 200 is provided. The open end is opened andclosed by a valve 28 a of the intake valve. The valve 28 a is connectedto a valve shaft 28 b that is vertically guided so as to move up anddown. The valve 28 a is designed to move between a valve openingposition and a valve closing position by an electromagnetic drive system30.

The electromagnetic drive system 30 includes a housing 300, a valveclosing core 301, a valve opening core 302, a valve closing coil 303, avalve opening coil 304, and an armature 305 that is carried by the valveshaft 28 b and moves between a valve closing electromagnetic devicehaving the valve closing core 301 and the valve closing coil 303 and avalve opening electromagnetic device having the valve opening core 302and the valve opening coil 304. The electromagnetic drive system 30further includes compression coil springs 306, 307 that serve toelastically bring the armature 305 into a center position between theelectromagnetic devices when no electric current is applied to the coils303 nor 304.

Referring to FIG. 1, an intake valve lift sensor 40 is directlyassembled onto the electromagnetic drive system 30. The lift sensor 40includes a housing 400 connected to the housing 300 of theelectromagnetic drive system 30, a disc-like target 401 attached to theupper end of the valve shaft 28 b within the housing 400, and a gapsensor 402 that is provided in the housing 400 so as to detectdisplacement of the target 401.

During operation of the internal combustion engine having theaforementioned electromagnetically driven intake valve, an appropriateelectric controller switches supply of electricity between the valveclosing coil and the valve opening coil in accordance with a rotatingphase of the crank shaft of the engine. As a result, the intake port isclosed by switching the supply of electricity to the intake valveclosing coil 303. The intake port is opened by switching the supply ofelectricity to the intake valve opening coil 304.

In the electromagnetic drive system including the cores, coils, armatureand springs, a positional deviation of the armature is not caused by thepositional restriction, that is, contour of the cam in operation butcaused by imbalance of the force. Accordingly opening and closing of thevalve operated in response to the electric command signals that commandopening and closing of the valve may deviate from a predetermined normalcharacteristic at every opening and closing valve operation in responseto the electric command signals. The valve is tightly seated on thevalve seat in the closed state in which friction force that is likely todisperse acts between the valve and the valve seat. Especially in thecase where an annular shoulder portion of the intake valve or theexhaust valve of the internal combustion engine abuts on the annularvalve seat along the respective center axes, the frictional force actingbetween the valve and the valve seat may vary depending on concentricityof those elements. The friction drag acting on the valve at a time whenthe valve is opened from the closed state may vary among a plurality ofvalves each being identically designed. Furthermore, the friction dragacting on the single valve may also vary at every opening and closingoperation. As the timing for opening the intake valve is partiallyoverlapped with the timing for closing the exhaust valve, a smalldifference in the valve opening characteristic may influence theoperation performance of the engine after the air intake state has beenchanged. Even if the intake valve opening timing is slightly deviatedfrom the control target value, the desired effect cannot be obtained inthe control for operating the engine.

The deviation of the valve opening operation from the normalcharacteristic may also occur in the exhaust valve owing to dispersionin the friction of engagement between the valve and the valve seat. Asthe opening operation of the exhaust valve is not overlapped with theopening operation nor closing operation of the intake valve, the slightdispersion in the opening characteristics of the exhaust valve may benegligible in view of controlling the operation of the internalcombustion engine.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a method of operatinginternal combustion engine including electromagnetically driven intakevalves, by which the problem caused by dispersion in characteristics ofthe operation of the intake valve, especially the electromagneticallydriven intake valve of the internal combustion engine.

According to an embodiment of the invention, a method of operating aninternal combustion engine having an electromagnetically driven intakevalve for a vehicle including detecting deviation of an openingoperation of the electromagnetically driven intake valve in response toa command signal for opening the intake valve from a predeterminedcharacteristic, and correcting at least one of parameters used forcontrolling operation of the internal combustion engine so as to reducea change in an intake air charging state in which the internalcombustion engine is charged with the intake air.

A valve closing timing or the intake valve or the exhaust valve thatcooperates with the intake valve may be used as a parameter to becorrected.

When the intake valve as the electromagnetically driven valve of theinternal combustion engine is operated in response to the electriccommand signal, the intake valve is not always considered as beingopened to coincide with the predetermined normal characteristic inresponse to the command signal. The actual opening operation of theintake valve is compared with the predetermined normal characteristic ofthe intake valve opening in response to the command signal so as todetect deviation from the normal characteristic. In order to reduce thechange in the intake air charging state in which the internal combustionengine is charged with the intake air owing to the aforementioneddeviation, at least one of parameters used for controlling operation ofthe internal combustion engine is corrected. This makes it possible toprevent the intake air charging state from deviating from a target valueowing to deviation of the actual opening operation of the intake valvefrom the predetermined normal characteristic in response to the valveopening command signal. As a result, the desired effect of controllingthe internal combustion engine can be obtained.

Assuming that at least one of parameters is a closing timing of theintake valve, correction of the closing timing of the intake valve mayreduce the change in the intake air charging state caused by deviationof the actual opening operation of the intake valve from the normalcharacteristic. Assuming that at least one of parameters is a closingtiming of the exhaust valve, correction of the closing timing of theexhaust valve may reduce the change in the air intake state caused bydeviation of the actual opening operation of the intake valve from thenormal characteristic.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of an example of an electrically drivenintake valve and a lift sensor combined with the intake valve;

FIG. 2 is a time chart showing each state in which electricity isapplied to coils for opening the valve and for closing the valve, andchange in the valve lift amount of the intake valve in response toapplication of electricity to the coils for opening the valve and forclosing the valve; and

FIG. 3 is a view showing a control structure employed to implement themethod of operating the internal combustion engine according to theinvention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 2 is a time chart showing each state in which electricity isapplied to coils for opening and closing the electromagnetically drivenintake valve, and change in the valve lift amount of the intake valve aselectricity is supplied to those coils. When the valve is closed,generally a holding electric current at a low level is applied to thecoil for closing the valve so as to keep the valve closed. The electriccurrent is cut at a time point t1 in order to open the valve, and theelectric current is reversely applied to the valve closing coil for ashort period until the time point t2 in order to release the valve fromthe closing position. The reversely applied electric current allows thearmature to be easily apart from the electromagnetic device for closingthe valve. Accordingly the valve is released from the valve seat thathas been tightly engaged with the valve with friction. Then the valve,valve shaft and the armature are altogether forced to move toward aneutral position as shown in FIG. 1. At a time point t3 when electricityis applied to the coil for opening the valve, the armature proceeds tothe valve opening direction passing over the neutral point. Afterpassing over the neutral point, the armature is moved toward theelectromagnetic device for opening the valve by the inertial force andelectromagnetic attraction force against the return biasing forcegenerated by the spring. At the time point t4, the valve is brought intoa full opening position. The electric current applied to the coil foropening the valve is switched to the holding current at the low level soas to keep the valve in the open state and maintained until the timepoint t5.

When a valve closing command signal is issued at the time point t5, thecurrent applied to the coil for opening the valve is cut, and current isreversely applied to the coil for opening the valve for a short perioduntil the time point t6 so as to move the armature away from the statewhere the valve is opened. The armature then is moved by the springforce toward the neutral point. When electric current application to thecoil for closing the valve is started at the time point t7, the armatureattracted by the electromagnetic device for closing the valve passesover the neutral point. Then the armature reaches the full closingposition of the valve at the time point t8 against the return force ofthe spring. Here the electric current applied to the coil for closingthe valve is further reduced to the holding current at a low level tokeep the valve closed.

Referring to the time chart shown in FIG. 2, the command signal tooperate the intake valve is represented by solid lines indicating thelevel of the electric current applied to the coils for closing andopening the valve. Meanwhile, the normal characteristic of the operationfor opening and closing the valve is represented by a solid lineindicating the change in the valve lift amount. In the state where thevalve is tightly seated on the valve seat, there is dispersion in thefrictional resistance generated between the valve and the valve seat atthe operation for opening the valve. Therefore, as shown by the dashedline of FIG. 2, the valve opening at the time point t1 to t4 in responseto the same valve opening command signal may deviate from the normalcharacteristic curve. The deviation indicated by the dashed line of FIG.2 is caused by the valve opening timing earlier than that of the normalcharacteristic when the holding electric current applied to the valveclosing coil is cut and the electric current is reversely applied at thetime point t1. The aforementioned deviation of the valve openingoperation is determined by the difference in time period taken forrelease of the friction engagement between the valve and the valve seat.The time difference is represented by the time lag generated at a momentwhen the valve lift rises up from 0. Consequently with the low valvelift, for example, L1 or higher, the dashed line indicating the actualvalve opening operation traces substantially the similar path of thesolid line indicating the normal characteristic along the time axis witha certain lag of time. This is because the low lift state is hardlyinfluenced by rise-up of the valve lift. Therefore deviation of thevalve opening operation from the normal characteristic may be detectedby obtaining a difference of time Δt between the time when the valvelift amount reaches a predetermined value that passes over the initialrise-up value, for example, L1 and the time set by the normalcharacteristic.

The deviation as aforementioned is used for correcting a certainparameter that relates to control of operating the internal combustionengine. Therefore, such deviation is desired to be detected at a stageas early as possible. It is thus preferable to obtain the aforementioneddeviation by comparing the time at which the predetermined low value ofthe valve lift, for example, L1 indicates a clear deviation with thecorresponding time set by the normal characteristic.

The deviation of the valve opening operation owing to dispersion in thefriction engagement between the valve and the valve seat tracessubstantially the similar path of the normal characteristic curve alongthe time axis with a certain lag of time. Accordingly the normalcharacteristic curve at the valve closing operation is shifted withrespect to the time axis so as to keep the intake air charging stateconstant in spite of the deviation. Therefore, in the case where thetiming for closing the intake valve is one of the parameters, suchparameter is corrected by shifting the timing at which the valve closingcommand signal is issued to the intake valve.

The deviation in the operation for opening the exhaust valve that iselectromagnetically driven may also be caused by the friction engagementbetween the valve and the valve seat. However, the opening operation ofthe exhaust valve is not overlapped with the operations for opening andclosing the intake valve. The deviation in the valve opening operationof the exhaust valve can be negligible in view of control for operatingthe internal combustion engine. Meanwhile, the exhaust gas recirculationrate in the intake stroke can be controlled by adjusting the timing forclosing the exhaust valve. This indicates that the deviation of theopening operation of the intake valve from the normal characteristiccurve may be compensated by correcting the timing for closing theexhaust valve when the internal combustion engine is operated whilerecirculating the exhaust gas. Therefore, it is possible to use thetiming for closing the exhaust valve as one of parameters to becorrected so as to cope with the deviation in the opening and closingoperation of the intake valve from the normal characteristic curve.

Incorporation of the device for changing a valve lift amount of theintake valve into the electromagnetically driven valve as shown in FIG.1 may correct the deviation of the opening and closing operation of theintake valve from the normal characteristic.

FIG. 3 shows elements that constitute the control structure used forimplementing the method for operating the internal combustion engineaccording to the invention. The internal combustion engine is controlledby the apparatus for controlling operation of the vehicle. Referring toFIG. 3, a controller 100 having a micro-computer receives inputs of asignal indicating an accelerator opening amount sent from an acceleratoropening sensor 1, a signal indicating an engine speed of the internalcombustion engine sent from an engine speed sensor 2, a signalindicating a vehicle speed sent from a vehicle speed sensor 3, a signalindicating a longitudinal acceleration of the vehicle sent from alongitudinal acceleration sensor 4, a signal indicating a temperature ofthe internal combustion engine sent from an engine coolant temperaturesensor 5, a signal indicating a rotational position of a crank shaftsent from a crank shaft angle sensor 6, a signal indicating an openingdegree of the intake valve sent from an intake valve lift sensor 7 (40in FIG. 1), and a signal indicating an opening degree of the exhaustvalve sent from an exhaust valve lift sensor 8. The controller 100controls a throttle valve 9 disposed in an intake passage of theinternal combustion engine, a fuel injection valve 10 for injecting fuelinto intake air in the internal combustion engine, an ignition coil thatactuates a spark plug, a coil 12 for closing the intake valve(corresponding to 303 in FIG. 1), a coil 13 for opening the intake valve(corresponding to 304 in FIG. 1), a coil for closing the exhaust valve,and a coil 15 for opening the exhaust valve based on the receivedsignals indicating operating conditions of the vehicle and the internalcombustion engine so as to momentarily determine how the internalcombustion engine is operated.

The intake valve is operated by the aforementioned control structure asshown in FIG. 2. The controller 100 operates calculation with respect tooperation of the vehicle, that is, the internal combustion engine basedon the operating state of the vehicle and the internal combustion enginerepresented by the signals sent from the sensors 1 to 8, and a controlprogram or a control map installed in the controller 100. The controller100 further transmits a control signal to operation elements such as thethrottle valve 9 and the like at a cycle time of several tensmilliseconds so as to control those elements.

The control method of operating the internal combustion engine of theinvention controls such that the electric current is applied to thecoils 12 and 13 for closing and opening the intake valve as shown by thesolid line of FIG. 2. In the aforementioned method, the current appliedto the coil 12 for closing the intake valve is switched from the holdingcurrent to the reversely applied current at the time point t1. Thecontroller maintains this state until the time point t2. Then thecontroller detects the time point when the valve lift amount becomes L1on the basis of the signal from the intake valve lift sensor 7. Thedetected time point is compared with the time point that is set to reachthe valve lift L1 in accordance with the normal characteristics curvebased on the time points t1 and t2 so as to calculate the timedifference Δt.

The controller 100 performs the feedforward control using the obtainedtime difference so as to correct the time point ts at which the holdingcurrent applied to the coil 13 for opening the intake valve is cut forclosing the intake valve, and to correct the time point t6 at whichreverse application of the current to the coil 13 is terminated as shownby the dashed line of FIG. 2 in accordance with the time difference. Thecontroller 100 further corrects the time point t7 at which applicationof the current to the coil 12 for closing the intake valve is startedand the time point t8 at which the application of the current to thecoil 12 is terminated in accordance with the time difference asindicated by the dashed line of FIG. 2.

The time difference in the opening operation of the intake valve iscompensated by correcting the closing operation of the exhaust valveduring operation of the internal combustion engine in which the exhaustgas is recirculated. In the case where the opening operation of theintake valve occurs earlier than the timing set by the normalcharacteristic, the closing operation set by the normal characteristicscurve is delayed as shown by the chain double-dashed line with respectto the actual valve closing of the exhaust valve as shown by the chainline of FIG. 2. By increasing amount of exhaust air compared with theintake air admitted into the cylinder chamber at the initial stage ofthe intake stroke, excessive admission of the intake air owing toearlier valve opening operation may be prevented even if the valveclosing of the intake valve is operated in accordance with the normalcharacteristic curve.

As described above, it is clear for those who skilled in the art that itis possible to perform various modification including correction of thevalve lift amount within the scope of the claim of the invention.

1. A method of operating an internal combustion engine including anelectromagnetically driven intake valve for a vehicle, the methodcomprising the steps of: detecting deviation of an opening operation ofthe electromagnetically driven intake valve in response to a commandsignal for opening the intake valve from a predetermined characteristic;and correcting at least one of parameters used for controlling operationof the internal combustion engine so as to reduce a change in an intakeair charging state in which the internal combustion engine is chargedwith the intake air.
 2. A method according to claim 1, wherein the atleast one of the parameters to be corrected comprises a valve closingtiming of the intake valve.
 3. A method according to claim 1, whereinthe internal combustion engine further includes an exhaust valve that iselectromagnetically driven, and wherein the at least one of theparameters to be corrected comprises a valve closing timing of theexhaust valve that cooperates with the intake valve.
 4. A methodaccording to claim 1, wherein the at least one of the parameters to becorrected comprises a valve lift amount of the intake valve.
 5. A methodaccording to claim 1, wherein the deviation of the opening operation ofthe electromagnetically driven intake valve is detected when the valvelift amount reaches a predetermined value after rise up of the valvelift amount.
 6. An internal combustion engine having anelectromagnetically driven intake valve comprising a controller that:detects deviation of an opening operation of the electromagneticallydriven intake valve in response to a command signal for opening theintake valve from a predetermined characteristic; and correcting atleast one of parameters used for controlling operation of the internalcombustion engine so as to reduce a change in an intake air chargingstate in which the internal combustion engine is charged with the intakeair.
 7. An internal combustion engine according to claim 6, wherein theat least one of the parameters to be corrected comprises a valve closingtiming of the intake valve.
 8. An internal combustion engine accordingto claim 6, further comprising an exhaust valve that iselectromagnetically driven, wherein the at least one of the parametersto be corrected comprises a valve closing timing of the exhaust valvethat cooperates with the intake valve.
 9. An internal combustion engineaccording to claim 6, wherein the at least one of the parameters to becorrected comprises a valve lift amount of the intake valve.
 10. Aninternal combustion engine according to claim 6, wherein the deviationof the opening operation of the electromagnetically driven intake valveis detected when the valve lift amount reaches a predetermined valueafter rise up of the valve lift amount.